Manufacturing method of thin component, bearing ring, thrust needle roller bearing, manufacturing method of rolling bearing ring, rolling bearing ring, and rolling bearing

ABSTRACT

A manufacturing method of a thin component is characterized by heating a thin component, and thereafter, while sizing with molds and using molds as cooling media, performing one of quenching and isothermal transformation processes on thin component. Thus, a manufacturing method of a thin component without warping or deformation in heat treatment with even and high hardness, a bearing ring, a thrust needle roller bearing, a manufacturing method of a rolling bearing ring, a rolling bearing ring, and a rolling bearing can be obtained.

TECHNICAL FIELD

The present invention relates to a manufacturing method of a thincomponent, a bearing ring, a thrust needle roller bearing, amanufacturing method of a rolling bearing ring, a rolling bearing ring,and a rolling bearing, and particularly, it relates to a manufacturingmethod of a thin component such as a ring of a thrust needle rollerbearing and a thin bearing ring, which tend to show great deformation inheat treatment and which are not subjected to polishing after the heattreatment.

BACKGROUND ART

Conventionally, for a ring of a thrust needle (needle) roller bearing ora ring of a drawn cup radial needle roller bearing, a low-carbon SPCC(JIS: a cold rolled steel plate) product, an SCM415 product (JIS: asteel product of chromium molybdenum steel) and the like carburized fora short period of time and a hardness-requiring portion of the surfacelayer is hardened have been used. Also, products of mid- to high-carbonsteel have been manufactured, such as an SK5 product (JIS: a steelproduct of carbon tool steel) subjected to through quenching by wholeheating. With all of these, carburizing or a batch type furnace havebeen used in heat treatment.

On the other hand, in some applications quenching of a thin product byhigh-frequency heating has also been performed. Conventionally, as toquenching of a thin product or an uneven-thickness component byhigh-frequency heating, there are techniques that can be found in thefollowing Patent Documents 1-4. All of these, however, employ air or gasfor cooling in quenching so as to control the cooling rate forsuppressing distortion, or to eliminate difference in quenching speedbetween a thick portion and a thin portion for suppressing deformation.

As to a tubular member, while there is a technique of providingconstraint in quenching can be found (for example, Patent Document 5),it employs a solution in quenching. Hence, there has been no techniqueemploying a mold for constraining and also as a quenching medium.

-   Patent Document 1: Japanese Patent Laying-Open No. 6-179920-   Patent Document 2: Japanese Patent Laying-Open No. 9-302416-   Patent Document 3: Japanese Patent Laying-Open No. 2001-214213-   Patent Document 4: Japanese Patent Laying-Open No. 2003-55713-   Patent Document 5: Japanese Patent Laying-Open No. 7-216456

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

With the conventional low-carbon SPCC or SCM415 product carburized for ashort period of time and a hardness-requiring portion of the surfacelayer is hardened is excellent in material workability. However, ascarburizing is employed in the heat treatment, the heat treatment isperformed off-line, and there have been problems that the life orstrength is not stabilized due to internal oxidation in carburizing orwarping or deformation in quenching.

The mid- to high-carbon steel such as the SK5 product is involved with aproblem that the material is high in hardness and that it is lessworkable. The products subjected to whole heating—quenching in anatmospheric furnace exhibit deformation due to uneven cooling, as can beseen in carburizing. Though slow and even cooling has been performed(for example, by blowing an inert gas for cooling) to such productssubjected to through quenching, it is difficult to eliminatedeformation, and tempering for correcting warping has been required toreduce warping.

As to the products subjected to high-frequency heating also, deformationin quenching cannot be avoided no matter how slowly the cooling isperformed, so long as air or water is used as a quenching medium in thesteps of high-frequency heating—water quenching. Particularly when wateris used, liquid replacement has been necessary due to deterioration orconsumption of the liquid.

Quenching by a mold can attain quenching without warping or deformationwhen associated with high-frequency heating. However, in a generaltechnique, a mold is not used as a refrigerant, and cooling by oil orwater, or drawing a product after oil quenching at a prescribedtemperature and constraining by a mold is performed.

Accordingly, an object of the present invention is to provide amanufacturing method of a thin component without warping or deformationin heat treatment (in quenching) and with even and high hardness, abearing ring, a thrust needle roller bearing, a manufacturing method ofa rolling bearing ring, a rolling bearing ring, and a rolling bearing.

Means for Solving the Problems

A manufacturing method of a thin component according to the presentinvention is characterized by heating a thin component, and thereafter,while sizing (correcting) with molds and using the molds as coolingmedia of the thin component, performing one of quenching and isothermaltransformation processes on the thin component.

Preferably, in the aforementioned manufacturing method of a thincomponent, the step of sizing the thin component with the molds includesthe step of pressing the thin component with the molds.

Preferably, in the aforementioned manufacturing method of a thincomponent, the quenching of the thin component is performed using themolds as quenching media.

Preferably, in the aforementioned manufacturing method of a thincomponent, the mold has cooling means, and the thin component cancontinuously be quenched by the molds.

Preferably, in the aforementioned manufacturing method of a thincomponent, the thin component is quenched in an atmosphere in whichoxidation of the thin component is prevented.

Preferably, in the aforementioned manufacturing method of a thincomponent, after the thin component is quenched, a tempering process isperformed on the thin component using the molds as temperaturecontrolling media.

Preferably, in the aforementioned manufacturing method of a thincomponent, the molds are used in both of the steps of quenching andtempering the thin component.

Preferably, in the aforementioned manufacturing method of a thincomponent, in the step of quenching the thin component, a moldingprocess of the thin component using the molds is concurrently performed.

Preferably, in the aforementioned manufacturing method of a thincomponent, the heating of the thin component is performed by inductionheating.

Preferably, in the aforementioned manufacturing method of a thincomponent, a material of the thin component is steel containing carbonby at least 0.4 mass %.

A bearing ring according to the present invention is manufactured by anyof the aforementioned methods.

A thrust needle roller bearing according to the present invention usesthe aforementioned bearing ring.

A manufacturing method of a rolling bearing ring according to thepresent invention is characterized by, after heating a rolling bearingring as the thin component using the aforementioned manufacturing methodof a thin component, by cooling the rolling bearing ring while pressingwith the molds and using the molds as quenching media, quenching therolling bearing ring.

Preferably, in the aforementioned manufacturing method of a rollingbearing ring, the heating of the rolling bearing ring is performed byinduction heating.

Preferably, in the aforementioned manufacturing method of a rollingbearing ring, the rolling bearing ring is mid-carbon steel containingcarbon by at least 0.4 mass %.

Preferably, in the aforementioned manufacturing method of a rollingbearing ring, in the quenching, a pressing pressure by the molds is atleast 2.94 N/cm².

A rolling bearing ring according to the present invention ischaracterized in that it is manufactured by any of the aforementionedmethods.

A rolling bearing according to the present invention includes theaforementioned rolling bearing ring and a rolling element.

Preferably, in the aforementioned rolling bearing, the rolling bearingis a thrust needle bearing.

EFFECTS OF THE INVENTION

The inventors of the present invention found that, in a manufacturingmethod of a thin component, by performing one of quenching andisothermal transformation processes on the thin component while pressingthe thin component with molds and using the molds as cooling media ofthe thin component, a bearing ring that does not exhibit deformation orwarping, that has an even hardness distribution, that is excellent intoughness, and that has long life can be manufactured.

As above, according to the manufacturing method of a thin component ofthe present invention, as warping and deformation are suppressed, a thincomponent can be manufactured with high precision. Further, as one ofquenching and isothermal transformation processes is performed usingmolds as cooling media, a process that requires less time and that iseven as compared to quenching by air-blow or oil can be attained. Bymaintaining the pressing pressure or temperature of the moldsconstantly, stable quality can be assured. Additionally, as no water oroil is used, working environment is clean and there will be noenvironmental pollution because of liquid waste or the like.

Still further, as the thin component is subjected to quenching orisothermal transformation process one by one, quality control isfacilitated.

When quenching, by using steel of a composition that can easily bequench-hardened, not to mention S53C (JIS: steel product of steel formachine structural use) that is the representative mid-carbon steel, theaforementioned quality can be achieved even when slow quench-hardeningis performed in the steps.

As to isothermal transformation, since transformation is caused byholding isothermally, the material of the thin component becomes abainite structure. Thus, as compared to a martensite structure, thereare advantages that less quenching distortion is resulted, toughness isattained without performing tempering, and secular dimensional change issuppressed. Further, as tempering is not necessary, a rolling bearingring can be subjected to heat treatment peace by peace. Still further,as tempering is not necessary, normal quenching and tempering can befinished with one process, and thus production steps are reduced. Stillfurther, by generating lower bainite, hardness can also be increased.

In the aforementioned manufacturing method of a thin component, asheating of the thin component is performed by induction heating, aninexpensive material for high-frequency use (steel for machinestructural use) can be applied, and the life thereof is stable.Additionally, since heating is performed by induction heating, heatingcan be achieved in a short period of time, and a surface irregular layersuch as with internal oxidation or decarburization will not be formed.Further, since heating is performed by induction heating, anon-quenching portion or non-isothermal transformation portion canpartially be formed by changing quenching conditions or the shape of acoil, and therefore the method can also be applied to a product thatrequires a bending process after heat treatment.

In the aforementioned manufacturing method of a thin component, the thincomponent can attain enough hardness by being mid-carbon steelcontaining carbon by at least 0.4 mass %.

By using the aforementioned thin component, a bearing ring with stablelife or strength and a thrust needle roller bearing using the same canbe obtained.

The inventors of the subject invention found that, in a manufacturingmethod of a rolling bearing ring, by quenching the rolling bearing ringby cooling the rolling bearing ring while pressing with molds and usingthe molds as quenching media, a bearing ring can be manufactured, whichhas an even hardness distribution, does not have defects such asoxidation or decarburization on the surface layer face, has very fewwarping and deformation, and has a long life. In this case, by usingsteel of a composition that can easily be quench-hardened, not tomention S53C (HS: steel product of steel for machine structural use)that is the representative mid-carbon steel, the aforementioned qualitywas achieved even when slow quench-hardening is performed in the steps.

As above, according to the manufacturing method of a rolling bearingring of the present invention, since warping and deformation can besuppressed, a thin bearing ring can be manufactured with high precision.Additionally, as quenching is performed using molds as quenching media,quenching that requires less time and that is even as compared toquenching by air-blow or oil can be attained. By maintaining thepressing pressure or temperature of the molds constantly, stable qualitycan be assured. Additionally, as no water or oil is used, workingenvironment is clean and there will be no environmental pollutionbecause of liquid waste or the like.

Further, as quenching is performed for one by one, quality control isfacilitated.

In the aforementioned manufacturing method of a rolling bearing ring, asheating of the rolling bearing ring is performed by induction heating,an inexpensive material for high-frequency use (steel for machinestructural use) can be applied, and the life thereof is stable.Additionally, since heating is performed by induction heating, heatingcan be achieved in a short period of time, and a surface irregular layersuch as with internal oxidation or decarburization will not be formed.Further, since heating is performed by induction heating, anon-quenching portion can partially be formed by changing quenchingconditions or the shape of a coil, and therefore the method can also beapplied to a process that requires a bending process after heattreatment.

In the aforementioned manufacturing method of a rolling bearing ring,the rolling bearing ring can attain enough hardness by being mid-carbonsteel containing carbon by at least 0.4 mass %.

In the aforementioned manufacturing method of a rolling bearing ring, bysetting the pressing pressure by the molds in quenching to at least 2.94N/cm², warping and distortion can effectively be suppressed.

By using the aforementioned rolling bearing ring, a rolling bearing withstable life or strength, for example a thrust needle roller bearing canbe obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing a step of heating arolling bearing ring in a manufacturing method of a thin component inone embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view showing a step of performingone of quenching and isothermal transformation processes on the rollingbearing ring in a manufacturing method of a thin component in oneembodiment of the present invention.

FIG. 3 is a schematic cross-sectional view showing a structure of athrust needle roller bearing using a rolling bearing ring in oneembodiment of the present invention.

FIG. 4 is a schematic cross-sectional view showing a structure of adrawn cup radial needle roller bearing using a rolling bearing ring inone embodiment of the present invention.

FIG. 5 is a schematic cross-sectional view showing a structure of adrawn cup radial needle roller bearing in which a plurality of rollerand cage assemblies are arranged in an outer ring.

DESCRIPTION OF THE REFERENCE SIGNS

1 thin component (rolling bearing ring), 2 rolling element, 3 cage, 4roller and cage assembly, 6, 7 collar portion, 10 rotary table, 10 aheat insulator, 11 heating coil, 12 a, 12 b mold, 13 weight.

BEST MODES FOR CARRYING OUT THE INVENTION

In the following, embodiment of the present invention will be describedbased on the drawings.

FIGS. 1 and 2 are cross-sectional views showing step by step amanufacturing method of a thin component according to one embodiment ofthe present invention. First, as a material, steel having a prescribedcomposition, for example mid-carbon steel containing carbon by at least0.4 mass % is prepared. This steel is subjected to a process of punchingor cutting of a plate-shape product or the like, to have a shape of arolling bearing ring as one example of a thin component. It should benoted that, in the present embodiment, a thin component specificallyrefers to a component of at most 3 mm thickness.

Referring to FIG. 1, a bearing ring 1 is placed on a heat insulator 10 aof a rotary table 10, and induction-heated by a heating coil 11, forexample. Here, bearing ring 1 is rotated by rotary table 10.

Referring to FIG. 2, bearing ring 1 heated to a prescribed temperatureis interposed between molds 12 a and 12 b, and a weight 13 is placed onmold 12 b. Thus, bearing ring 1 is subjected to quenching process orisothermal transformation process, while being pressed (sized) by molds12 a, 12 b with a pressing pressure of at least 2.94N/cm² (0.3 kgf/cm²),for example, and using molds 12 a, 12 b as cooling media. In otherwords, molds 12 a, 12 b constrain bearing ring 1 and serve as quenchingmedia in quenching bearing ring 1, or as isothermal transformation mediain isothermal transformation.

After quenching bearing ring 1, bearing ring 1 may be tempered in thestate constrained by molds 12 a, 12 b. In this case, molds 12 a, 12 bserve as tempering media in tempering bearing ring 1.

Through the aforementioned method, bearing ring 1 can be manufactured,which has an even hardness distribution, does not have defects such asoxidation or decarburization on the surface layer face, has very fewwarping and deformation, and has a long life.

As compared to a conventional bearing ring manufactured using air or gasas a quenching medium, rolling bearing ring 1 manufactured as above haslow and aligned flatness, and also has stabilized hardness.

It should be noted that, when quenching bearing ring 1, there is amethod to substantially increase the heat capacity of molds 12 a, 12 bas compared to that of bearing ring 1, as molds 12 a, 12 b are used asquenching media. For example, in order to suppress the temperatureincrease of molds 12 a, 12 b by at most 5 C.° for lowering thetemperature of bearing ring 1 by 900 C.°, the heat capacity of molds 12a, 12 b must be at least 180 times as great as that of bearing ring 1.As bearing ring 1 is interposed between upper and lower molds 12 a, 12b, the heat capacity of either upper mold 12 a or lower mold 12 b mustbe at least 90 times as great as that of bearing ring 1. Accordingly,provided that bearing ring 1 and molds 12 a, 12 b are formed of the samematerial (for example, steel) and have the same specific heat, then themass of either upper mold 12 a or lower mold 12 b must be at least 90times as great as that of bearing ring 1. If a substance of great heatcapacity, for example water, is allowed to flow through the molds, themolds themselves may be small.

If heating/quenching is performed in the air, even for a short period oftime, a thin component may be oxidized. Thus, an oxide film may beformed, the surface hardness may be decreased due to decarburization, orprecipitation of troostite may occur. A product such as a ring of athrust needle roller bearing, which is not subjected to finishing(polishing, super finishing) by a machine process after heat treatment,requires heat treatment (quenching) for suppressingoxidation/decarburization. Such heat treatment can be addressed by usingan inert gas in the atmosphere.

As quenching or isothermal transformation, in which molds are employedas cooling media as in the present embodiment, is a heat treatment ofpiece-by-piece, it is not necessary to separate the heat treatmentprocess from a production line as in a conventional manner, but insteadit may be incorporated into the production line of a machine process.Further, if tempering is performed by high-frequency induction heatingor high-frequency heating while performing pressing with molds(high-frequency press-tempering), there is an advantage of integratingthe whole processes from material input to product completion into aline.

In light of improving a processing speed, an efficient continuousquenching is possible by performing quenching while constantly coolinginside of the molds or the pressing surface with water, oil, air or thelike. To this end, it is preferable to provide cooling means forintroducing medium such as water, oil, air or the like into the molds.

It should be noted that, while tests were conducted in examplesdescribed below with plate-like products of 1 mm thickness, the methodof the present invention is applicable to a thick plate (a 5-6 mmthickness plate) if the pressure when pressing is increased, though thethickness for quench-hardening at the cooling rate by the molds may belimited.

The molding process of a flange or a collar can simultaneously beperformed when quenching, by controlling the shape of the mold or thepressing pressure.

Using bearing ring 1 manufactured by the aforementioned method, a thrustneedle roller bearing, for example as shown in FIG. 3, can bemanufactured. This thrust needle roller bearing has a pair of bearingrings 1, and a plurality of rolling elements 2 (needle rollers) arrangedbetween the pair of bearing rings 1, and a cage 3 for rollably holdingthe plurality of rolling elements 2.

Additionally, using bearing ring 1 manufactured by the aforementionedmethod, a drawn cup radial needle roller bearing, for example as shownin FIG. 4, can also be manufactured. This drawn cup radial needle rollerbearing has a cylindrical outer ring 1 that is bearing ring 1, and aroller and cage assembly 4 arranged on the internal periphery side ofouter ring 1. Roller and cage assembly 4 has a plurality of rollingelements (needle rollers) 2, and a cage 3 for rollably holding theplurality of rolling elements 2. While collar portions 6, 7 are arrangedon the opposing ends of outer ring 1, one of or both of collar portions6, 7 may be eliminated. Additionally, as shown in FIG. 5, a plurality of(or two) roller and cage assemblies 4 may be arranged on the internalperiphery side of outer ring 1, as shown in FIG. 5.

As bearing ring 1 shown in FIG. 4 or 5 is cylindrical outer ring 1,cooling molds used in quenching outer ring 1 must be in a shapedifferent from that of molds 12 a, 12 b shown in FIG. 2, i.e., forexample a cylindrical shape.

While the case in which a thin component is a bearing ring of a thrustneedle roller bearing has been described in the foregoing, the presentinvention is not limited thereto and it may be a washer or a leaf springthat is employed in a wearing portion.

EXAMPLE

In the following, examples of the present invention will be described.

Example 1

Mid-carbon steel S53C was used as a material, and a thrust needle rollerbearing ring (NTN product name: AS1112) having an outer shape of innerdiameter 60 mm, outer diameter 85 mm, and thickness 1 mm wasmanufactured by punching from a plate-like product.

Using a high-frequency induction heating apparatus (80 kHz) and rotatingthe ring, induction heating was performed by allowing prescribed currentto flow through an induction coil arranged closely to one end panel(FIG. 1). In this case, heating was conducted slowly in order for theentire ring to attain a uniform temperature (approximately 900° C.).Thereafter, the ring was set in upper and lower press molds made of ironand having a heat capacity substantially greater than that of the ring,the ring was immediately pressed by pressing at a prescribed pressureand transformation-hardened through mold cooling by pressing (FIG. 2).Varying mold temperature at transformation-hardening and constraint timeby the molds, the relationship between hardness and microstructure wasexamined.

Table 1 shows relationship among mold temperature and constraint time(holding time) by molds, pressing pressure, warping deformation,hardness after heat treatment, and microstructure.

Table 1 also shows relationship among warping deformation, hardnessafter heat treatment, and microstructure of a sample that washigh-frequency heated and thereafter water quenched, a sample that waswholly heated and thereafter air-blow quenched, and a sample that washigh-frequency heated and air-cooled.

TABLE 1 Quality of Samples After Heat Treatment Press Cooling orQuenching Pressing Warping Steel Mold Holding Pressure DeformationHardness Type Temperature Time (N/cm²) (μm) (HV) Structure Example ofS53C 250 1 min 2.94 16 745 TM + LB Present 300 1 min 2.94 18 730 TM + LBInvention 320 1 min 2.94 18 685 LB 300 5 min 2.94 18 710 LB 300 30 sec2.94 19 730 TM + LB 30 1 min 2.94 20 750 M Comparative S53CHigh-Frequency Heated, Without >250 740 M Example Thereafter WaterQuenched Pressing Wholly Heated, Thereafter Without 48 710 M Air-BlowQuenched Pressing High-Frequency Heated, Without 29 510 T ThereafterAir-Cooled Pressing Structure: TM refers to tempered martensite, LBrefers to lower bainite, M refers to quenched martensite, T refers totroostite

From the result shown in Table 1, it can be seen that, as in the exampleof the present invention, with the pressing pressure of 2.94N/cm² (0.3kgf/cm²), by setting the mold temperature to at least 250° C. and atmost 320° C. and the constraint time (holding time) by molds to at least30 seconds and at most 5 minutes, isothermal transformation occurs and astructure having lower bainite can be obtained. It can also be seenthat, in the structure of the example of the present invention havinglower bainite, warping deformation becomes at most 19 μm, and Vickershardness HV becomes at least 685. Further, in part of the example of thepresent invention, a structure similar to tempered martensite thatappears on tempering was observed, while tempering was not performed.

Additionally, it can be seen that, as in the example of the presentinvention, when continuous cooling was performed by setting the moldtemperature to 30° C. and the constraint time (holding time) by molds to1 minute, martensite transformation occurs and a structure havingtempered martensite can be obtained. It can also be seen that, in thissample, warping deformation becomes 20 μm, and Vickers hardness HVbecomes 750.

As above, it has been shown that, with all samples of the presentinvention, warping deformation becomes at most 20 μm, and Vickershardness HV becomes at least 685.

On the other hand, samples of the comparative example were in a qualityin which warping deformation was more than 20 μm and which cannot attainVickers hardness of at least HV 685.

As to the representative of these bearing rings, result of performinglife estimation with the condition shown in Table 2 is shown in Table 3.

TABLE 2 Thrust Bearing Life Test Condition Bearing Ring NTN Product NameAS1112(φ60 × φ85 × t1) Cage, Roller Half (twenty-four) of Rollers of NTNProduct Name AXK1112 Number of 5000 rpm Revolutions Bearing Load 9.8 kNLubricating Oil VG10 Oil Film Parameter 0.101 Calculated Life 11.3 h(Considering Oil Film Parameter) Number of Test 6 pieces Specimens

TABLE 3 Life Test Result of Samples Press Cooling or Quenching SteelHeat Mold Holding Life Test Result Type Treatment Temperature TimeL10(h) L10 ratio Example of S53C High- 250 1 min 19.3 1.2 PresentFrequency 300 1 min 16.5 1.0 Invention Heating 320 1 min 15.2 1.0 300 5min 16.9 1.1 300 30 sec 17.2 1.1 30 1 min 15.8 1.0 Comparative S53CHigh-Frequency Heated, Without Test Impossible Due to Example ThereafterWater Quenched Pressing Great Deformation Wholly Heated, ThereafterWithout L10 = 11.9 h Air-Blow Quenched Pressing High-Frequency Heated,Without Test Impossible Due to Thereafter Air-Cooled Pressing LowHardness

Here, since the ring of the example of the present invention subjectedto isothermal transformation is partially or wholly subjected toisothermal transformation, tempering was not performed.

The rings of the example of the present invention subjected tomartensite transformation by continuous cooling quenching were subjectedto tempering of 150° C.×120 minutes. The test was conducted under ascarce lubrication condition.

From the result of Table 3, it can be seen that L10 life of the samplesof the example of the present invention was at least 15.2 hours, whichwas increased. The sample of the comparative example, which washigh-frequency heated normally and thereafter water quenched, was sodeformed that it could not be tested. The sample of the comparativeexample, which was wholly heated and thereafter air-blow quenched,exhibited 11.9 hours of L10 life, which was reduced. Despite being athin component, the sample of the comparative example, which washigh-frequency heated and thereafter air-cooled, was notquench-hardened.

From the result above, with the ring obtained by the present method (theexample of the present invention), warping deformation can besuppressed, and hardness and life can be increased as compared to thecomparative example.

Example 2

As materials, mid-carbon steel S53C and steel of a composition that isimproved in quenching property and that can attain sufficient hardnesswith slow cooling (0.7 mass % C—1.0 mass % Si—0.6 mass % Mn—1.5 mass %Cr—0.3 mass % Mo) were used.

From these materials, thrusts needle bearing ring (NTN product name:AS1112) having an outer shape of inner diameter 60 mm, outer diameter 85mm, and thickness 1 mm was manufactured by cutting.

Using a high-frequency induction heating apparatus (80 kHz) and rotatingthe ring, induction heating was performed by allowing prescribed currentto flow through an induction coil arranged closely to one end panel(FIG. 1). In this case, heating was conducted slowly in order for theentire ring to attain a uniform temperature (approximately 900° C.).Thereafter, the ring was set in upper and lower press molds made of ironand having a heat capacity substantially greater than that of the ring,the ring was immediately pressed by pressing at a prescribed pressureand quench-hardened through mold cooling by pressing (FIG. 2). In thiscase, by setting the pressing-pressure to at least approximately2.94N/cm², deformation/warping in quenching-hardening was prevented. Thetime required for quench-hardening (the cooling time until normaltemperature was attained) was approximately two second. The mass of oneof upper and lower press molds used this time was 3.4 kg at thelightest. As the mass of the ring was 22 g, the heat capacity of one ofthe press molds was approximately 150 times as great as that of thering.

Table 4 shows deformation state of conventional various products anddeformation state in the experiment conducted this time.

TABLE 4 Quality of Samples After Heat Treatment Pressing Warping SteelHeat Pressure Distortion Hardness Type Treatment Quenching (N/cm²) (μm)(HV) Example of S53C High- Press- 0.98 47 730 Present FrequencyQuenching Invention Heating High- Press- 2.94 20 760 Frequency QuenchingHeating High- Press- 9.80 19 770 Frequency Quenching Heating 0.7% CHigh- Press- 0.98 75 750 Steel Frequency Quenching Heating High- Press-2.94 52 780 Frequency Quenching Heating High- Press- 9.80 48 775Frequency Quenching Heating Comparative S53C High- Water Without 690 740Example Frequency Quenching Pressing Heating SCr 415 Carburizing Oil 830730 Quenching SPCC Carburizing Oil 715 730 Quenching SK5 Whole Oil 650760 Heating Quenching SCr 415 Carburizing Air-Blow 99 730 Quenching SK5Whole Air-Blow 78 750 Heating Quenching

From the result of Table 4, while conventional air-blow quenchingproducts show few warping, deformation or warping of the productsaccording to the present method still show smaller degree than theair-blow quenching products, irrespective of the steel types.Accordingly, distortion correction or warping correction after heattreatment is not necessary. By setting pressing-pressure to at least aprescribed value, deformation was suppressed to at most a certain value.It should be noted that, as actual quenching is not quenching usingwater soluble cooling agent or oil, the periphery of the quenchingmechanism can be maintained clean, eliminating waste liquid processes.

After performing the aforementioned quenching to the test rings,tempering at 150° C. for two hours was performed, and finishing processwas performed on the surface thereof. Thus, the rings were subjected tolife estimation. The test was conducted under a scarce lubricationcondition. The rolling life test condition was the same as the conditionshown in Table 2. The test result is shown in Table 5.

TABLE 5 Life Test Result of Samples Pressing Steel Heat Pressure L10life Life Type Treatment Quenching (N/cm²) (h: hour) Ratio Example ofS53C High- Press- 2.94 15.8 1.0 Present Frequency Quenching InventionHeating High- Press- 9.80 17.7 1.1 Frequency Quenching Heating 0.7% CHigh- Press- 2.94 25.6 1.6 Steel Frequency Quenching Heating High-Press- 9.80 27.9 1.8 Frequency Quenching Heating Comparative S53C High-Water Without Test Example Frequency Quenching Pressing ImpossibleHeating Due to SCr 415 Carburizing Oil Great Quenching Warping SPCCCarburizing Oil Quenching SK5 Whole Oil Heating Quenching SCr 415Carburizing Air-Blow Without 15.9 1.0 Quenching Pressing SK5 WholeAir-Blow 13.8 0.9 Heating Quenching

From the result of Table 5, in the rings according to the present methodthat provides less warping deformation, even S53C attained the life ofthe conventional carburized product level. 0.7 mass % C steel attainedlonger life than the carburized steel. This may be attributed to itshigher content of C as compared to S53C, which facilitates attaininghigh hardness. Additionally, it is considered that much Si, Mo, and Crcontent contributed to the long life. The thin races in the shape of thepresent case exhibited great warping deformation with free quenching byoil or water, and therefore life test could not be conducted.

From the result above, with the rings (example of the present invention)obtained through the present method, warping deformation was suppressedas compared to the comparative example, and the life thereof can beincreased.

It should be understood that the embodiment and examples disclosedherein are illustrative and non-restrictive in every respect. The scopeof the present invention is defined by the terms of the claims, ratherthan the description above, and is intended to include any modificationswithin the meaning and scope equivalent to the terms of the claims.

INDUSTRIAL APPLICABILITY

The manufacturing method of the present invention is advantageouslyapplied to a manufacturing method of a thin component, such as a ring ofa thrust needle roller bearing or a thin bearing ring, which tends toshow great deformation in heat treatment and to which a polishingprocess after the heat treatment is not performed.

1-11. (canceled)
 12. A thrust needle roller bearing including a bearingring manufactured by a method of a thin component, the method includingthe steps of heating said thin component, and thereafter, while sizingwith molds and using said molds as cooling media of said thin component,performing one of quenching and isothermal transformation processes onsaid thin component. 13-17. (canceled)
 18. A rolling bearing, comprisinga rolling bearing ring and a rolling element, wherein said rollingbearing ring is manufactured by a manufacturing method comprising thestep of after heating a rolling bearing ring as a thin component using amanufacturing method of said thin component by cooling said rollingbearing ring while pressing with molds and using said molds as quenchingmedia, quenching said rolling bearing ring, and the manufacturing methodof the thin component including the steps of heating a thin component,and thereafter, while sizing with molds and using said molds as coolingmedia of said thin component, performing one of quenching and isothermaltransformation processes on said thin component.
 19. The rolling bearingaccording to claim 18, wherein said rolling bearing is a thrust needleroller bearing.